1. Field of the Invention
The present invention relates to a Group III nitride semiconductor light-emitting device and to a method for producing the same. More particularly, the present invention relates to a Group III nitride semiconductor light-emitting device in which a piezoelectric field generated in the light-emitting layer is relaxed, and to a method for producing the same.
2. Background Art
Generally, Group III nitride semiconductor light-emitting devices are produced through epitaxial growth of a Group III nitride semiconductor from a growth substrate. In this process, a plurality of Group III nitride semiconductor layers having different lattice constants is formed. Due to the lattice constant difference, stress generates in a relevant semiconductor layer. The stress generates a piezoelectric field, which declines the potential of the quantum well of the light-emitting layer, thereby spatially separating electrons from holes. As a result, the probability of recombination between electrons and holes in the light-emitting layer decreases. In this case, light emission efficiency of the semiconductor light-emitting device drops.
In order to counteract the piezoelectric field generated in the light-emitting layer, some techniques have been developed. Japanese Patent Application Laid-Open (kokai) No. 2007-305965 discloses a technique of forming a Si-doped GaN layer adjacent to an InGaN layer as a well layer (refer to FIG. 6). The GaN layer generates an electric field in the opposite direction to the piezoelectric field, and relaxes the strain of the InGaN layer as the well layer.
However, when the GaN layer is doped with Si, the crystal quality of the GaN layer is comparatively deteriorated. The deteriorated crystal quality is inherited by the well layer formed on the GaN layer. Thus, the crystal quality is deteriorated due to the formation of Si-doped GaN layer, causing a reduction in the light emission efficiency. In other words, the effect to counteract the piezoelectric field is in a trade-off relation with the achievement of high crystal quality.
The present inventors founded that the piezoelectric field can be counteracted while preventing the deterioration of crystal quality by forming a Si-doped InGaN layer having a small In composition ratio instead of the Si-doped GaN layer. In the InGaN layer having a small In composition ratio, In atoms easily migrate even at a low-temperature. Therefore, the crystal quality is not much deteriorated by Si doping.